Question

sin^2x-sinx-1=0
solve for x

Answer 1

this is a quadratic in terms of sin(x)
replace sin(x) with u
it might make it easier for you see that

Answer 2

\[(\sin(x))^2-\sin(x)-1=0 \\ u^2-u-1=0\]
solve for u
then replace u with sin(x)
and solve for x